In long endless conveyor belts of the type having a body formed from an electrically insulating material, used to convey bulk material, there is a possibility of encountering a rip in the belt. Rips may occur, for example by sharp objects being dropped upon the belt at a loading station. It is desirable to promptly detect particularly longitudinal rips and, preferably, to shut down and repair the conveyor belt upon such detection, thereby reducing the possibility for damage to the belt.
In prior structures as described, for example, in U.S. Pat. No. 3,792,459 a conveyor belt rip detection system is disclosed of a type having a plurality of spaced antennae imbedded transversely at spaced-apart locations in the belt to periodically couple an electrical signal from a transmitter probe to a receiver probe while the belt, with its respective antennae, moves past the probes. The detected electrical signals function to monitor the integrity of the belt and to shut down the conveying system in response to a break in an antenna which would be typically indicative of a longitudinal rip in the belt. Detection of the antenna break permits belt repair or replacement before the break or rip elongates and destroys an extended portion or even the entirety of the belt or before the conveyor belt assembly ceases to function properly as a consequence of the rip. A rip, noted timely, can be corrected with relatively minimal cost and inconvenience.
In prior devices it has been the general practice to utilize antennae made of metallic screens or wires such as steel wires, extending transversely across the width of the belt, at spaced apart distances. Such screen or wire antennae function properly during normal operations for a period of time.
Frequently, however, due to movement of the belt and wires around conveyor rollers in the conveyor system, continued flexing stresses upon the screen or wires of the antennae may cause premature breakage of the wires, thus causing a malfunction in the rip detection system Metallic wires are also susceptible to breakage caused by ore dropped on the belt at a loading station. A broken antenna, caused by a failure of any nature, undesirably will give the appearance to a conveyor belt control system that a rip exists in the belt. The control system could then improperly shut down the conveying system when in fact no such rip exists in the belt. Alternate decisional programming of the control system may also be employed.
The electrical signals, in the form of charges, are readily conveyed across the belt through the antennae as the antennae move past the probe sites. Such charges must traverse non-conductive zones such as an air space between the probes and the adjacent surface of the belt and then through any belt segments interposed between the probes and the angennae where the antennae are imbedded within the belt. The movement of the charges through these non-conductive zones tend to decrease the signal to noise ratio of the signal being carried from probe to probe. These electrically non-conductive zones decrease the system reliability, thus permitting mistaken signals, or signals of inconsistent intensity, to be received by the detector probe in implementing the rip detection function.
Priorly, as described in U.S. Pat. No. 4,296,855 issued to Gary L. Blalock, antennae have been constructed of a knit or woven, carbon infused non-metallic fiber such as nylon. Such antennae have performed satisfactorily having mechanical properties superior to metallic screen type antennae.